To achieve warm-white luminous colors, U.S. Pat. No. 5,694,002 has disclosed a metal halide discharge lamp which contains a metal halide fill comprising the metals Na, Sc, Li, Dy and Tl with a warm-white luminous color. The color temperature is 3000 K.
Fills of this type comprising scandium have a poor maintenance, which means that the luminous flux drops considerably during the operating time. Moreover, the color rendering of scandium-based lamps is relatively poor, in particular in the red spectral region.
GB 1 316 803 has disclosed a metal halide lamp which uses a metal halide fill which as emitter uses one of the iodides of Tl, Sc, Ca, Cs, Dy, Na, Sn, La, Li and Ba. The buffer gas used is one of the metal iodides of Sb, As, Bi, In, Zn, Cd or Pb. The buffer gas is used in particular to set the electrical properties of the discharge. By contrast, there is no discussion of the buffer gases influencing the color rendering. Only fills comprising the buffer gases ZnI2 and CdI2 are specifically presented. In an exemplary embodiment comprising ZnI2 as buffer gas, optional small quantities of mercury are also taken into consideration as a second buffer gas.
US-A 2003/0141818 makes use of fills comprising halides of Ca and complex-forming halides of Al and/or Ga to improve the red rendering in lamps with color temperatures below 4000 K. Further components, in addition to mercury and noble gas, are halides of Dy, Ho, Tm, Na, Li, Cs.
U.S. Pat. No. 4,742,268 uses fills comprising Ca iodide, thallium iodide and Sn iodide in elliptically shaped discharge vessels made from quartz glass in order to achieve a very good color rendering.